JPH01169757A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To improve coercive force and the square shape of a magnetic Kerr curve by forming a recording layer of artificial lattice films which are alternately laminated with a specific atomic layer number of Co and Pt and are specified in the total thickness thereof on a substrate on which an underlying ZnS film is formed. CONSTITUTION:The underlying ZnS layer 2 is formed on the glass substrate 1 and the recording layer 3 consisting of the Co-Pt artificial lattice films which are alternately laminated with Co 0.5-2.5atom. layers and Pt 1-7atom. layers and have 50-500Angstrom total thickness is formed on this layer 2. The range of the atomic layer number of the respective layers and the total thickness suppresses generation of an intra-surface magnetization component and optimizes magneto-optical characteristics. The coercive force and the square shape of the magnetic Kerr curve are improved and the shape of pits at the time of recording is sharpened; in addition, the S/N of reading out is improved by forming the recording layer 3 via the underlying ZnS layer 2 on the substrate in such a manner. The magneto-optical recording with high quality at a high density is thereby enabled.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a magneto-optical recording medium that uses magneto-optic effects to record and reproduce information using laser beams, etc. Concerning an excellent magneto-optical recording medium.

[Summary of the invention] The present invention provides a 0.5 to 2.5 atomic layer of Co, F'd and/or
Or Ptl~7 atomic layers are alternately laminated with a total thickness of 50
~500 In a magneto-optical recording medium having an artificial lattice film as a recording layer, the recording layer is formed on a substrate via a ZnS undercoating film to align the coercive force and the square shape of the magnetic Kerr curve, This makes it possible to increase the S/N ratio during continuous output.

[Conventional technology]

2. Description of the Related Art In recent years, a magneto-optical recording method in which recording and reproduction is performed using semiconductor laser light or the like has been attracting attention as a rewritable high-density recording method.

The recording material used in this magneto-optical recording method is G
Rare earth elements such as d, Tb, and Dy, and Fe.

A typical conventional example is an amorphous alloy in combination with a transition element such as Co. However, the rare earth elements and Fe that constitute these amorphous alloy thin films are highly oxidized and have the property of easily combining with oxygen in the air to form oxides. If such oxidation progresses and leads to corrosion or pitting, it will cause the signal to drop out, and especially if rare earth elements are oxidized,
The S/N ratio deteriorates as the coercive force and the Kerr rotation angle of the residual magnetic field decrease. Such problems are unavoidable as long as rare earth elements are used as the material for the recording layer of a magneto-optical recording medium.

In contrast, the present inventors have previously developed a method that does not contain rare earth elements,
CON and P
Special training on magneto-optical recording media whose recording layer is a superlattice metal film laminated with t-layer and/or PdN
It is disclosed in Specification No. 9 etc.

(Problems to be Solved by the Invention) However, in order to put magneto-optical recording media into practical use in the future, it is necessary to further improve the coercive force, the magnetic Kerr rotation angle, and the rectangular shape of the magnetic Kerr curve.

Therefore, the present invention aims to further improve the magneto-optical properties of such a magneto-optical recording medium, and particularly aims to improve the coercive force and the squareness of the magnetic Kerr curve.

[Means for solving problems]

As a result of intensive research to achieve the above-mentioned objective, the present inventors have found that by laminating ZnS as an underlayer of a magneto-optical recording medium, the coercive force and the squareness of the magnetic Kerr curve can be significantly improved. I found it.

The magneto-optical recording medium according to the present invention has been completed based on this knowledge, and has a total thickness of 0.5 to 2.5 atomic layers of Co and 7 to 7 atomic layers of Pd and/or Ptl alternately laminated. An artificial lattice film of 50 to 500 people is used as a recording layer,
The recording layer is formed on a substrate with a ZnS underlayer interposed therebetween.

First, the artificial lattice film that can be used as a recording layer in the magneto-optical recording medium according to the present invention is a Go-PL superlattice film in which a Co layer and a Ptl are laminated, and a Co-Pd-based artificial lattice film in which a Co layer and a Pd layer are laminated. The superlattice film is a Co-Pt-Pd system superlattice film in which a Co layer and a Pt-Pd alloy layer are laminated, or a combination of a Co layer, a Pt layer, and a Pd layer is laminated. Here, the range of the number of atomic layers in each layer mentioned above was set from the perspective of optimizing the magneto-optical properties, and in any case, outside the above range, an in-plane magnetization component will occur and the magneto-optical properties will deteriorate. do. Furthermore, it is preferable that the total thickness of the recording layer is 50 to 500 mm.

Note that the interface between each metal layer constituting the above-mentioned superlattice film is
Ideally, atoms of different metals should be formed flat without mixing with each other, creating a so-called superlattice structure.
The so-called modulation structure (&llll
may have a metamorphic structure).

The artificial lattice film can be formed by sputtering, vacuum deposition, molecular beam epitaxy (MBE), or the like.

The superlattice film also contains Af, Si, Ti, V, Cr, and Mn for the purpose of lowering the Curie point.

Fe, Ni, Cu, Zn, Ga, Ge, Zr.

Nb, Mo, Ru, Rh, Ag, In, Sn.

Sb, Hf, Ta, W, Re, Os, Ir, Au.

At least one of the elements Pb and Bi may be added as appropriate.

In the magneto-optical recording medium of the present invention, prior to forming the recording layer as described above, a ZnS base film is first formed on a suitable substrate such as glass by sputtering, vacuum evaporation, MBE, or the like. The thickness of this ZnS base film is selected within the range of 5 to 5,000 layers. If it is smaller than the above range, the desired effect as a base film cannot be obtained,
Moreover, if it is larger than the above range, there is a risk that the magneto-optical properties will deteriorate, and it is not practical from the viewpoint of productivity and economy. A more preferable range is 5 to 1000 people.

The basic structure of such a magneto-optical recording medium is shown in FIG. 1, in which a recording layer (3) is formed on a substrate (1) with a ZnS underlayer (2) interposed therebetween.

However, in practice, as shown in FIG.
On top of this, a metal reflective film such as Al, Au, Pt, Cu, etc.
4) is generally provided. In order to further improve the magneto-optical properties, as shown in FIG.
Another dielectric layer (5) may be provided on top. ZnS may be used as the material for the dielectric layer (5) at this time, but A2□Os, TaxOs, MgO, SiO
t, T i Ox, F egos.

Oxide-based dielectrics such as Z r Ox, B i g03,
Or Z r N, T i N, S 1sNa,
Al1N, BN.

Nitride-based dielectrics such as TaN and NbN can also be used. Even in such a case, it is practically desirable to further provide a metal reflective film (4) on the dielectric layer (5) as shown in FIG.

In addition to a light beam, a method for writing to the recording layer of a magneto-optical recording medium having the above-mentioned configuration uses a nail-shaped magnetic head, a thermal pen, an electron beam, etc., which can supply the energy necessary to generate reversed magnetic domains. Needless to say, anything is fine as long as it is something.

[Effect]

The magneto-optical recording medium according to the present invention has excellent corrosion resistance because the recording layer does not contain a rare earth element. Furthermore, the recording layer is made of Zn.
Since it is formed on the substrate via the S underlayer, the coercive force and the squareness of the magnetic Kerr curve are improved. If the coercive force and the square shape of the magnetic Kerr curve are improved in this way, the shape of the bit during recording becomes sharper, and the S/N ratio during reading improves. Furthermore, if the thickness of the ZnS underlayer is optimally selected, an increase in the magnetic Kerr rotation angle (enhancement effect) due to interference can be expected.

〔Example〕

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

This example is an example of a magneto-optical recording medium in which a Go--Pt superlattice film is used as a recording layer, and the recording layer is formed on a glass substrate with a ZnS underlayer interposed therebetween.

First, a ZnS sintered tablet was placed in a high vacuum evaporation apparatus, and ZnS base films of various thicknesses were deposited on a glass substrate under a vacuum of 2 Xl0-' Torr.

Next, a 100 m
CO and PL targets with a diameter of m were installed, and the Z
The above glass substrate on which the nS base film was formed was placed. Here, binary simultaneous magnetron sputtering was performed in an argon atmosphere with a gas pressure of 5 Xl0-'Torr.
A Co--Pt based superlattice film, which will become a recording layer, was formed on the ZnS base film. According to this device, the period of the artificial lattice film can be arbitrarily determined by changing the current or power applied to each target or the rotational speed of the rotating base on which the glass substrate is placed. In this example, C
DC sputtering with input current of 0.40A for O target, input power of 400A for Pt target.
A Co--Pt superlattice film with a total thickness of 100 layers was prepared by high-frequency sputtering of W, and the rotational speed of the rotating base was set at 16 rpm to prepare each sample of each magneto-optical recording medium.

The period of the created Co-Pt superlattice film is X
It was determined from the peak angle in small-angle line scattering.

For comparison, a magneto-optical recording medium without a ZnS underlayer was also produced in the same manner.

The magneto-optical characteristics of each of these magneto-optical recording media were measured from the substrate side using a magnetic Kerr curve measuring device, and the results are shown in FIGS. 5(A) and 5(B).

Figure 5 (A) shows the case where 600 ZnS base films are provided.
FIG. 5(B) corresponds to a case where no ZnS underlayer is provided as a comparative example, and the vertical axis in the figure is the magnetic Kerr rotation angle θ, (°
), the horizontal axis represents the magnetization strength H (Oe), respectively. First, the magnetic Kerr rotation angle θ when no Zn5T layer is provided.
, is 0,58° and the coercive force is 162.50 e. On the other hand, it is clear that when a ZnS underlayer is provided, not only the coercive force and the magnetic Kerr rotation angle increase, but also the squareness is improved.

FIG. 6 shows the relationship between the thickness of the ZnS underlayer and the coercive force in the same magneto-optical recording medium. In the figure, the vertical axis is the coercive force (O
e) The horizontal axis represents the thickness (in thickness) of the ZnS base film. From this figure, it can be seen that the ZnS underlayer already has a significant coercive force increasing effect when it is formed as thin as about 50 layers.

FIG. 7 further shows ZnS in the same magneto-optical recording medium.
The relationship between the thickness of the base film and the magnetic Kerr rotation angle is shown. In the figure,
The vertical axis represents the coercive force (Oe), and the horizontal axis represents the film thickness (Oe) of the ZnS underlayer. Looking at this figure, it can be seen that at a film thickness of around 600 Oe, which corresponds to the case shown in Figure 5 (A), The magnetic Kerr rotation angle shows a maximum value, suggesting that an effect of increasing the magnetic Kerr rotation angle can be expected when the thickness of the ZnS underlayer is optimally selected.

Incidentally, a similar effect was also observed in a magneto-optical recording medium having a Co--Pd superlattice film as a recording layer.

Further, the above ZnS underlayer can also be applied to a magneto-optical recording medium having a Go-PL-Pd based artificial lattice film as a recording layer.

〔Effect of the invention〕

As is clear from the above explanation, in the magneto-optical recording medium according to the present invention, the coercive force and the squareness of the magnetic Kerr curve are improved, so the shape of the bit during recording becomes sharper, and when The S/N ratio of is improved. moreover,
If the thickness of the ZnS base film is optimally selected,
An increase in the magnetic Kerr rotation angle due to interference (enhancement effect) can also be expected. Therefore, high-quality and high-density magneto-optical recording becomes possible.

Furthermore, since the artificial lattice film does not contain rare earth elements whose supply is expected to become tight worldwide in the future, a stable and economical supply of magneto-optical recording media can be expected.

If such a magneto-optical recording medium is used as a storage medium for a magneto-optical memory such as a so-called beam-addressable file memory, which writes using a light beam and reads using the magnetic Kerr effect, it can achieve extremely high performance. It is possible to realize a memory device that has a high density, a high S/N ratio, and maintains high reliability over a long period of time.

[Brief explanation of the drawing]

FIG. 1 is a schematic sectional view showing the most basic structure of a magneto-optical recording medium according to the present invention. 2 to 4 are schematic sectional views showing other configuration examples of the magneto-optical recording medium according to the present invention, in which FIG. 2 shows an example in which a metal reflective film is provided on the recording layer, and FIG. 3 shows an example in which a metal reflective film is provided on the recording layer. FIG. 4 shows an example in which a dielectric layer is provided on the recording layer, and FIG. 4 shows an example in which a dielectric layer and a metal reflective film are provided in this order on the recording layer. Figure 5 (A) and Figure 5 (
B) is a magnetic Kerr curve showing the change in magneto-optical properties depending on the presence or absence of a ZnS underlayer in a magneto-optical recording medium in which a Co-PL superlattice film is formed on a glass substrate; When having a ZnS base film with a thickness of 600 mm,
FIG. 5(B) shows the case where no ZnS base film is present. FIG. 6 is a characteristic diagram showing the change in coercive force depending on the thickness of the ZnS underlayer in a rotary magnetic recording medium. Figure 7 shows the W! FIG. 3 is a characteristic diagram showing changes in magnetic Kerr rotation angle depending on thickness. 1...Substrate 2...ZnS base film 3...Recording layer 4...Metal reflective film 5...Dielectric layer Patent applicant Sony Corporation representative Patent attorney Koike Mimi Ei Tamura - Same Masaru Sato Figure 1 Figure 3 Figure 2 Figure 4 Magnetic tension car rotation mountain (0) Coercion n (Oe)

Claims (1)

[Claims] Co0.5-2.5 atomic layer and Pd and/or Pt
Total thickness of 50 to 500 Å with 1 to 7 atomic layers stacked alternately
A magneto-optical recording medium comprising an artificial lattice film as a recording layer, and the recording layer is formed on a substrate with a ZnS underlayer interposed therebetween.